AASHTO HB-17 DIVISION II SEC 1-2002 Division II Construction - Structure Excavation and Backfill《结构挖掘和回填》.pdf

1、1.1 GENERAL Section 1 STRUCTURE EXCAVATION AND BACKFILL Structure excavation shall consist of the removal of all material, of whatever nature, necessary for the construc- tion of foundations for bridges, retaining walls, and other major structures in accordance with the plans or as di- rected by the

2、 Engineer. If not otherwise provided for in the contract, struc- ture excavation shall include the furnishing of all neces- sary equipment and the construction and subsequent removal of all cofferdams, shoring, and water control systems which may be necessary for the execution of the work. It shall

3、also include, if not otherwise specified, the placement of all necessary backfill, including any neces- sary stockpiling of excavated material which is to be used in backfill, and the disposing of excavated material, which is not required for backfill, in roadway embankments or as provided for exces

4、s and unsuitable material in Subsec- tion 203.02, AASHTO Guide SpeciJications for Highway Construction. If the contract does not include a separate pay item or items for such work, structure excavation shall include all necessary clearing and grubbing and the re- moval of existing structures within

5、the area to be exca- vated. Classification, if any, of excavation will be indicated on the plans and set forth in the proposal. The removal and disposal of buried natural or manmade objects are included in the class of excavation in which they are located, unless such removal and disposal are includ

6、ed in other items of work. However, in the case of a buried manmade object, if (I) its removal requires the use of methods or equipment not used for other excavation on the project, (2) its presence was not indicated on the plans or in the special provisions, (3) its presence could not have been asc

7、ertained by site investigation, including contact with identified utilities within the area, and (4) the Contractor so requests in writing prior to its removal, the removal and disposal of such object will be paid for as extra work, and its volume will not be included in the measured quantity of exc

8、avation. 1.2 WORKING DRAWINGS Whenever specified, the Contractor shall provide working drawings, accompanied by calculations where appropriate, of excavation procedures, embankment con- struction and backfilling operations. This plan shall show the details of shoring, bracing, slope treatment or oth

9、er protective system proposed for use and shall be accompa- nied by design calculations and supporting data in suffi- cient detail to permit an engineering review of the pro- posed design. The working drawings and plans for protection from caving shall be submitted sufficiently in advance of pro- po

10、sed use to allow for their review, revision, if needed, and approval without delay to the work. Working drawings must be approved by the Engineer prior to performance of the work involved and such ap- proval shall not relieve the Contractor of any responsibil- ity under the contract for the successf

11、ul completion of the work. 1.3 MATERIALS Material used for backfill shall be free of frozen lumps, wood or other degradable matter and shall be of a grading such that the required compaction can be consistently ob- tained using the compaction methods selected by the Con- tractor. Permeable material

12、for underdrains shall conform to AASHTO Guide Specijcations for Highway Construc- tion, Subsection 704.01. 1.4 CONSTRUCTION 1.4.1 Depth of Footings The elevation of the bottoms of footings, as shown on the plans, shall be considered as approximate only and the Engineer may order, in writing, such ch

13、anges in dimen- sions or elevation of footings as may be necessary to se- cure a satisfactory foundation. 477 478 HIGHWAY BRIDGES 1.4.2 1.4.2 Foundation Preparation and Control of Water 1.4.2.1 General All substructures, where practical, shall be constructed in open excavation and, where necessary,

14、the excavation shall be shored, braced, or protected by cofferdams con- structed in accordance with the requirements contained in Article 3.3, “Cofferdams and Shoring.” When footings can be placed in the dry without the use of cofferdams, backforms may be omitted with the approval of the Engi- neer,

15、 and the entire excavation filled with concrete to the required elevation of the top of the footing. The additional concrete required shall be furnished and placed at the ex- pense of the Contractor. Temporary water control systems shall conform to the requirements contained in Article 3.4, “Tempora

16、ry Water Control Systems.” 1.4.2.2 Excavations Within Channels When excavation encroaches upon a live stream bed or channel, unless otherwise permitted, no excavation shall be made outside of caissons, cribs, cofferdams, steel pil- ing, or sheeting, and the natural stream bed adjacent to the structu

17、re shall not be disturbed without permission from the Engineer. If any excavation or dredging is made at the site of the structure before caissons, cribs, or cofferdams are sunk or are in place, the Contractor shall, without extra charge, after the foundation base is in place, backfill all such exca

18、vation to the original ground surface or river bed with material satisfactory to the Engineer. Material tem- porarily deposited within the flow area of streams from foundation or other excavation shall be removed and the stream flow area freed from obstruction thereby. 1.4.2.3 Foundations on Rock Wh

19、en a foundation is to rest on rock, the rock shall be freed from all loose material, cleaned and cut to a firm sur- face, either level, stepped, or roughened, as may be di- rected by the Engineer. All seams shall be cleaned out and filled with concrete, mortar, or grout before the footing is placed.

20、 Where blasting is required to reach footing level, any loose, fractured rock caused by overbreak below bearing level shall be removed and replaced with concrete or grouted at the Contractors expense. 1.4.2.4 Other Foundations When a foundation is to rest on an excavated surface other than rock, spe

21、cial care shall be taken not to disturb the bottom of the excavation, and the final removal of the foundation material to grade shall not be made until just before the footing is to be placed. Where the material below the bottom of footings not supported by piles has been disturbed, it shall be remo

22、ved and the entire space filled with concrete or other approved material at the Contractors expense. Under footings sup- ported on piles, the over-excavation or disturbed volumes shall be replaced and compacted as directed by the Engi- neer. 1.4.2.5 Approval of Foundation After each excavation is co

23、mpleted, the Contractor shall notify the Engineer, and no concrete or other footing material shall be placed until the Engineer has approved the depth of the excavation and the character of the foun- dation material. 1.4.3 Backfill Backfill material shall conform to the provisions of Ar- ticle 1.3.

24、If sufficient material of suitable quality is not available from excavation within the project limits, the Contractor shall import such material as directed by the Engineer. All spaces excavated and not occupied by abutments, piers, or other permanent work shall be refilled with earth up to the surf

25、ace of the surrounding ground, with a suffi- cient allowance for settlement. Except as otherwise pro- vided, all backfill shall be thoroughly compacted to the density of the surrounding ground, and its top surface shall be neatly graded. Fill placed around piers shall be deposited on both sides to a

26、pproximately the same eleva- tion at the same time. Rocks larger than 3 inches maxi- mum dimension shall not be placed against the concrete surfaces. Embankment construction shall conform to the re- quirements of Subsection 203.02, AASHTO Guide Spec- $cations for Highway Construction. The fill at re

27、taining walls, abutments, wingwalls, and all bridge bents in em- bankment shall be deposited in well-compacted, horizon- tal layers not to exceed 6 inches in thickness and shall be brought up uniformly on all sides of the structure or facil- ity. Backfill within or beneath embankments, within the ro

28、adway in excavated areas, or in front of abutments and retaining walls or wingwalls shall be compacted to the same density as required for embankments. No backfill shall be placed against any concrete struc- ture until permission has been given by the Engineer. The placing of such backfill shall als

29、o conform to the require- ments of Article 8.15.2, “Earth Loads.” The backfill in front of abutments and wingwalls shall be placed first to prevent the possibility of forward movement. Jetting of 1.4.3 DIVISION II-CONSTRUCTION 479 the fill behind abutments and wingwalls will not be per- mitted. Adeq

30、uate provision shall be made for the thorough drainage of all backfill. French drains, consisting of at least 2 cubic feet of permeable material wrapped in filter fabric to prevent clogging and transmission of fines from the backfill, shall be placed at weep holes. Backfilling of metal and concrete

31、culverts shall be done in accordance with the requirements of Sections 26, “Metal Culverts,” and 27, “Concrete Culverts.” 1.5 MEASUREMENT AND PAYMENT 1.5.1 Measurement The quantity to be paid for as structure excavation shall be measured by the cubic yard. The quantities for payment will be determin

32、ed from limits shown on the plans, in- cluded in the specifications, or ordered by the Engineer. No deduction in structure excavation pay quantities will be made where the Contractor does not excavate material which is outside the limits of the actual structure but within the limits of payment for s

33、tructure excavation. In the absence of plans or special provisions indicating pay limits for structure excavation, the horizontal limits will be vertical planes 18 inches outside of the neat lines of footings or structures without footings; the top limits shall be the original ground or the top of t

34、he required grad- ing cross section, whichever is lower; and the lower lim- its shall be the bottom of the footing or base of structure, or the lower limit of excavation ordered by the Engineer. When foundations are located within embankments and the specifications require the embankment to be con-

35、structed to a specified elevation which is above the bottom of the footing or base of structure prior to construction of the foundation, then such specified elevation will be con- sidered to be the original ground. When it is necessary, in the opinion of the Engineer, to carry the foundations below

36、the elevations shown on the plans, the excavation for the first 3 feet of additional depth will be included in the quantity for which payment will be made under this item. Excavation below this additional depth will be paid for as extra work, unless the Contrac- tor states in writing that payment at

37、 contract prices is ac- ceptable. 1.5.2 Payment Unless otherwise provided, structure excavation, mea- sured as provided in Article 1.5.1, will be paid for by the cubic yard for the kind and class specified. Payment for structure excavation shall include full compensation for all labor, material, equ

38、ipment, and other items that may be necessary or convenient to the success- ful completion of the excavation to the elevation of the bottom of footings or base of structure. Full compensation for controlling and removing water from excavations and for furnishing and installing or con- structing all

39、cofferdams, shoring, and all other facilities necessary to the operations, except concrete seal courses which are shown on the plans, and their subsequent re- moval, shall be considered as included in the contract price for structure excavation, unless the contract pro- vides for their separate paym

40、ent. The contract price for structure excavation shall in- clude full payment for all handling and storage of exca- vated materials which are to be used as backfill, including any necessary drying, and the disposal of all surplus or un- suitable excavated materials, unless otherwise provided for in

41、the contract. Any clearing, grubbing, or structure re- moval which is required, but not paid for under other items of the contract, will be considered to be included in the price paid for structure excavation. Unless the contract provides for its separate payment, the contract price for structure excavation shall include full compensation for the placing and compacting of structure backfill. The furnishing of backfill material from sources other than excavation will be paid for at the con- tract unit price for the material being used, or as extra work if no unit price has been established.